About the Author: (from The American Mathematical Monthly, vol. 97 (1990)) Donald G. Saari received his undergraduate degree from Michigan Technological University and his Ph.D. in mathematics from Purdue University. His Ph.D. dissertation, written under the guidance of Harry Pollard, concerned the qualitative behavior of dynamics in the general Newtonian N-body problem. After a postdoctoral position in the Yale Astronomy Department, Saari moved to Northwestern University where he currently is Professor of Mathematics. His main research interests revolve around applications of dynamical systems to celestial mechanics and physics and to issues coming from the social sciences.